Wafer chucking apparatus and method for spin processor

ABSTRACT

A wafer chuck is configured to hold a wafer efficiently for spin process cleaning of wafer edges and back sides. A first group of retractable tips extend to hold the wafer during a first portion of the cleaning period. A second group of retractable tips extend to hold the wafer during a second portion of the cleaning period. Residues left between the tips and the wafer edge areas during the first portion of the cleaning period are removed during the second portion. The change from the first group of tips to the second group of tips occurs while the wafer is rotating.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods and apparatus for cleaningdeposits from a semiconductor wafer. More particularly, the presentinvention relates to methods and apparatus for chucking a wafer forcleaning deposited films and flakes from the edge and bevel portions ofa semiconductor wafer.

2. Description of the Related Art

Semiconductor wafer fabrication involves a series of processes used tocreate semiconductor devices and integrated circuits (ICs) in and on asemiconductor wafer surface. Fabrication typically involves the basicoperations of layering and patterning, together with others such asdoping, and heat treatments. Layering is an operation used to add thinlayers of material (typically insulator, semi-conductor or conductor) tothe surface of the semiconductor wafer. Patterning is an operation thatis used to remove specific portions of the top layer or layers on thewafer surface.

Once the integrated circuits on the wafer are completed, i.e., layeringand patterning are implemented, the wafer is conventionally sliced intosections known as die. A large number of wafers are diced from a wafer,typically 100 to 1000. A wafer may comprise as many as 10 or morelayers, each layer formed in a separate step. During processing ofsemiconductor wafers, films (i.e., layers) are deposited not only on theselected areas of the wafer surface designated for the die, but also onthe margin of the wafer, i.e., the wafer edge and the bevel. The filmsmay also be deposited on the backside of the wafer near the edge. Thesefilms located at or near the edge may become problematic duringsubsequent processing, such as occurring when the edge deposits begin toflake or peel off. This may result in contamination during subsequentprocess steps. For example, such flakes may cause a bridge between twoconductors or prevent the formation of a pattern. The flaking maytherefore cause processing defects which may result in die failure attest.

As integrated circuit devices grow smaller, higher conductance and lowercapacitance is required of the interconnects. In order to accommodatethese objectives, the trend has been towards the use of copper forinterconnects and damascene methods for forming the interconnects inlow-k dielectric materials. But fabrication processes that use copperinterconnects require higher levels of cleanliness for the edge, beveledregions and back side of the wafer to prevent contamination ofsubsequent process steps.

One method for cleaning these deposits involves a spin processor, i.e.,placing the wafer on a chuck and spinning the wafer at high speeds whileselectively dispersing one or more chemicals over the wafer surface. Buttypically spin processors hold wafers at the wafer edge with tips thatare nail like. With this method, any copper contamination locatedbetween the tips of the chuck and the wafer bevel or edge cannot becompletely cleaned. Moreover, the tips of the chuck adversely influencethe cleaning efforts directed to the backside off the wafer bydisturbing the chemical flow.

Accordingly, it is desirable to provide a more effective method andapparatus for removing films from the bevel and edge of a wafer. Thus,what is needed is an improved wafer holder and method for holding awafer during spin process cleaning.

SUMMARY OF THE INVENTION

To achieve the foregoing, the present invention provides methods andapparatus for holding a wafer during the cleaning of the edge and backsides of a wafer during the manufacture of semiconductor integratedcircuits. A wafer chuck rotates the wafer at high speeds during singlewafer spin process cleaning steps directed to the edge, bevel, andbackside of the wafer. In order to rotate the wafer while minimizing theinfluence of the chuck on chemicals directed to the wafer, retractabletips extend to the wafer edge. The tips are divided into groups so thatduring one part of the spin process cleaning, a first group of tipsengage the edge of the wafer. During a second part of the cleaning step,a second group of tips are extended to the wafer edge to hold the wafer.Shortly thereafter, the first tips are retracted to permit cleaning ofdeposits or flakes located at the points of contact between the firstgroup of tips and the wafer edge. With this arrangement, completecleaning of the entire wafer edge, bevel, and backside areas may beperformed without flakes or other deposit remnants contaminating futureprocess steps.

According to one embodiment of the present invention, a wafer chuck forsupporting a wafer during spin process cleaning of a wafer includes afirst plurality of retractable tips for engaging the edge of the wafer.The wafer chuck also includes a second plurality of retractable tips,also for engaging the edge of the wafer. Each of the pluralities areconfigured so that in a first state the first plurality of tips isengaged with the edge of the wafer and the second plurality is retractedfrom the edge of the wafer. The tips are further configured so that in asecond state, the first plurality of tips are not engaged with the edgeof the wafer while each the second plurality of tips is engaged.

According to another embodiment of the present invention, the waferchuck includes further a third plurality of retractable tips. In thisembodiment, the first, second, and third pluralities of retractable tipsare further configured so that in a in a third state the first andsecond pluralities of retractable tips are retracted from the edge ofthe wafer while the third plurality of retractable tips is engaged withthe edge of the wafer.

These and other features and advantages of the present invention aredescribed below with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic top view of a wafer chuck in accordance withone embodiment of the present invention.

FIG. 2 is a flowchart illustrating a method of holding a wafer forcleaning the edge areas of a wafer in accordance with one embodiment ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to preferred embodiments of theinvention. Examples of the preferred embodiments are illustrated in theaccompanying drawings. While the invention will be described inconjunction with these preferred embodiments, it will be understood thatit is not intended to limit the invention to such preferred embodiments.On the contrary, it is intended to cover alternatives, modifications,and equivalents as may be included within the spirit and scope of theinvention as defined by the appended claims. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. The present inventionmay be practiced without some or all of these specific details. In otherinstances, well known process operations have not been described indetail in order not to unnecessarily obscure the present invention.

The present invention provides improved methods and apparatus for usinga wafer chuck to hold a wafer during spin processing. These embodimentsmay be used during the cleaning and etching of the edge and back side ofa wafer during the manufacture of semiconductor integrated circuits. Atypical objective is to clear a 2 mm portion from the edge of the waferinward. A spin processing apparatus in accordance with one embodiment ofthe present invention is constructed with retractable tips engaging theedge of the wafer and extending from the wafer chuck. In order to rotatethe wafer while minimizing the influence of the chuck on chemicalsdirected to the wafer, retractable tips extend to the wafer edge. Thetips are divided into groups so that during one part of the spin processcleaning, a first group of tips engages the edge of the wafer. During asecond part of the cleaning step, a second group of tips is extended tothe wafer edge to hold the wafer. Shortly thereafter, i.e., shortlyafter the second group is extended, the first tips are retracted topermit cleaning of deposits or flakes located at the points of contactbetween the first group of tips and the wafer edge. With thisarrangement, complete cleaning of the entire wafer edge, bevel, andbackside areas may be performed without flakes or other deposit remnantscontaminating future process steps.

FIG. 1 illustrates a diagrammatic top view of a wafer chuck system 100in accordance with one embodiment of the present invention. According tothis embodiment, the wafer 102 is positioned for spin processing bywafer chuck tips 104–109. The wafer chuck tips 104–109 are formed in twogroups according to one embodiment of the present invention. That is, afirst group of wafer chuck tips 104, 106, and 108 are arranged equallyto surround the wafer. That is, the wafer tips are preferably spaceduniformly around the circumference of the wafer when holding the wafer.A second grouping of chuck tips, wafer chuck tips 105, 107 and 109 arealso arranged equally around the periphery of the wafer and arranged toengage the wafer edge.

Preferably, the first group of chuck tips are engaged for a portion ofthe clean (etch) cycle and the second grouping of chuck tips are engagedduring at least the remaining portion of the clean cycle. That is, eachof the first and second grouping of chuck tips have a duty cycle of lessthan 100%. Preferably the duty cycle for the first group will overlapsomewhat the duty cycle of the second group to enable better stabilityin transfer of handling responsibilities from the first group of chucktips to the second group of chuck tips during the spin processing.

Techniques for extending chuck tips to hold a wafer and drivingmechanisms for driving chuck tips are known to those of skill in the artand thus the examples provided in the description are included only forillustration purposes and are not intended to limit the invention. Thechuck tips may be driven by any suitable means for controllablyextending the chuck tips into position for holding the wafer. Forexample, drive units 114–119 as illustrated in FIG. 1 may be connectedto any suitable means for positioning the wafer chuck tips to hold thewafer. For example, the wafer chuck tips may be extended by anyelectromagnetic, hydraulic, pneumatic, or mechanical means, as known tothose of skill in the relevant art. The drive units 114–119 are shown ingeneral diagrammatic form to illustrate their general coupling to thewafer chuck tips 104–109, and not to indicate any particular form ofdrive unit. Typically, actuators and connecting linkage and other forcetransfer mechanisms utilized in moving the wafer tips into position andto maintain pressure on the wafer are located within the body of thechuck 103 below the back surface of the wafer. Embodiments of thepresent invention are intended to extend to include any and all types ofdrive mechanisms, irrespective of their locations within the chuck.

Moreover, although wafer chuck tips may typically be extended in adirection substantially parallel to the axis of rotation of the waferand chuck, the embodiments of the invention are not so limited. Forexample, embodiments of the present invention are intended to apply alsoto wafer chuck tips which extend either partially or completely in alateral direction (i.e., towards the edge of a held wafer in the planeof the wafer).

Each of the drive units may be individually controlled or alternativelycontrolled in groups. That is, the drive units may be controlled bysuitable controllers so that each of the chuck tips belonging to agrouping extend substantially simultaneously. Preferably, in anembodiment where the wafer chuck tips are configured to engage the waferin two different groupings, i.e., a first grouping for a first timeinterval of the etch cycle and a second grouping for a second timeinterval of that etch cycle, two independent drive units will beprovided. For example, the first grouping of wafer chuck tips may beextended by a common drive unit with the second grouping extended by asecond common drive unit.

Of course, with the benefit of the guidance provided in thisspecification, one skilled in the art could configure wafer chuck tipshaving independent drive mechanisms for each tip, for exampleindividually controlled electromagnetic drives, to extend in groups. Forexample, such responses can individually be programmed by a controllerconnected to the individual drive units for each tip. Thus, theembodiments of the present invention are intended to extend to all suchvariations where the extension and retraction of wafer chuck tips to andfrom the wafer occurs in two or more independently controllable groups.That is, by incorporating at least two independent chucking drives,wafer chucks as described in embodiments of the present invention areable to more effectively and efficiently perform etching during spinprocessing.

According to an alternative embodiment of the present invention, thechuck tips are positioned around the periphery of the wafer so that thechuck tips are extended and retracted in one of three separate groups.As discussed above, in this alternative embodiment there will preferablybe some overlap so that when groups of three wafer chuck tips areutilized, the duty cycle (i.e., the portion of the complete cleaningcycle) for each such state will exceed 33.33% by a slight amount, suchas for example, a duty cycle of 35–40%.

It is recognized that some finite period of time may be necessary forthe chuck tips to extend to a position where they are engaged with thewafer and conversely a like period of time for the chuck tips to retractfrom their extended position, i.e., in contact with the wafer to a fullyretracted position. Variations in the control signal to accommodate thetime periods are within the ability of one of skill in the art andtherefore will not be described further here.

Although embodiments have also been described with wafer chuck tipshaving a “nail-like” shape, the invention is not so limited. Althoughminimizing the contact area between the wafer and the chuck tips ispreferable, the apparatus and techniques of the present invention inchanging engagement of the tips between groups of tips permits greaterflexibility in the shape of the wafer chuck tip. That is, wafer chucktips which have shapes that adversely affect the flow of etchantchemicals can be used, the effect minimized due to the changingengagements (i.e., extensions) between the groups of tips. For example,larger tips or tips configured in clamp-like shapes may be used. Thus,embodiments of the present invention may be used with a variety of waferchuck tip shapes.

FIG. 2 is a flowchart illustrating a method 200 of cleaning a wafer inaccordance with one embodiment of the present invention. The wafercleaning or etching process 200 begins at a step 202 with selection of asingle wafer for further processing. Next, at a step 204, the wafer istransferred to the spin processor. Wafer transfer is effectuated with atransfer arm holding both the chuck and the wafer. For purposes ofillustration of this embodiment, the wafer chuck is described as having6 wafer tips, arranged in two groups. That is, the wafer chuck tips arearranged uniformly around the perimeter of the wafer but activated ineither a first group or a second group. This example is provided forillustration purposes and is not intended to be limiting. Duringtransfer, all of the six tips engage the wafer.

Next, during step 206, the wafer is placed in a centering position withall (six) of the tips locking. It should be appreciated that inaccordance with one embodiment, transfer of the wafer and chuck by thetransfer arm occurs with the wafer retained by the wafer tips in apartially extended position, i.e., the wafer tips acting to hold thewafer without being fully extended into a locking position.Alternatively, the wafer and chuck may be transferred with all tipslocking the wafer in position.

In a subsequent step 208, the first group of tips maintain their lockedposition (i.e., fully extended) while the second group of tips isunlocked (i.e., retracted).

Next, in step 210, wafer rotation starts and etching commences.Typically, an etchant chemical is dispersed over selected areas of thewafer to perform the etching. Thus, during the initial part of theetching cycle, the wafer is held by the first group of tips.

After approximately half of the etching time is completed the secondgroup of tips are extended (i.e. locked) and the first group of tipsretract (i.e., unlock) in step 212. This changeover occurs with thewafer still rotating. With this arrangement, it is not necessary to stoprotation of the wafer in order to change the wafer location relative tothe tips. Accordingly, process time is reduced.

Next the rinse step 214 is completed followed by the drying step 216.For each of these steps, preferably the second group of tips continue tobe extended to engage the wafer. The process ends at a step 218. Thus,by changing the engagement of the tips from a first group to a secondgroup with the wafer still rotating, better etching performance isachieved by decreasing the adverse influence of the tips. Preferably,the wafer will be retained by 6 wafer chuck tips, acting in groups ofthree. Preferably, the wafer chuck tips will be spaced uniformly aroundthe perimeter (i.e., circumference) of the wafer, although the inventionis not so limited. In an alternative embodiment, nine wafer chuck tipsare available to retain the wafer, acting in groups of three. That is,changeover of holding tips (i.e., changing engagement of the tips fromone group to another) occurs twice during the etch cycle in thisalternative embodiment. The first changeover occurs form the first groupof 3 tips to the second group of 3 tips and the second changeoverinvolves a change from the second group to the third group of tips. Inthis embodiment, three independent chucking drives are employed.

In yet another alternative embodiment, the sequence of groups of tipsengaged with the wafer tips is configured so that the tip changeoveroccurs twice during the etch step, but with only two groups of tipsused. That is, for example, the first group of tips are initiallyextended during the etch cycle, followed by extension of the secondgroup (and the retraction of the first group), followed by extension ofthe first group again (and retraction of the second). Of course manydifferent variations are possible with the concepts and guidanceprovided by the invention and the scope of the present invention isintended to extend to include those variations. Although describedpreferably as using 3 tips in each group to engage the wafer, theinvention is not so limited. Any number of tips may constitute a group.For example, the first group or plurality of tips may include 6 tips toengage the wafer whereas the second group may include 4 tips.

The embodiments of the present invention have generally been describedwith reference to a spin process cleaning of a wafer edge but should notbe interpreted as limiting the invention. It should be appreciated thatthe embodiments of the present invention may be adapted to work withother semiconductor processes where a wafer chuck rotates a wafer aspart of the process. Minor modifications may be performed to enablethese adaptations within the knowledge of those of skill in the art.

By using the apparatus and methods of the present invention, etching ofthe top edge, backside edge, and bevel of the wafer may be performed toremove films that may flake off during subsequent wafer processing afterthin film deposition, etching, or photo masking steps. Further, by usingthis apparatus, edge etching may be performed in a single step process,without the need to remove and reposition the wafer during the cleaning.By avoiding the stopping of the rotation of the chuck to reposition thewafer, unnecessary drying steps may be avoided. Thus, the describedapparatus and methods enable effective cleaning of the edge, bevel, andbacksides of the wafer and shortens the process time.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

1. A method for cleaning a wafer by rotating the wafer while dispersinga chemical over the wafer surface, the method comprising: extending afirst plurality of retractable wafer chuck tips from a wafer chuck in adirection substantially parallel to the axis of rotation of the waferchuck to engage a wafer edge with the first plurality of tips; rotatingthe wafer with the first plurality of tips engaged; extending a secondplurality of retractable wafer chuck tips from the wafer chuck in adirection substantially parallel to the axis of rotation of the waferchuck to engage the edge of the rotating wafer with the second pluralityof tips; disengaging the first plurality of tips from the edge of therotating wafer after the second plurality of tips are engaged with theedge of the wafer.
 2. The method for cleaning a wafer as recited inclaim 1, wherein the first plurality of tips is engaged by a first drivemechanism and the second plurality of tips is engaged by a second drivemechanism, the second drive mechanism configured to actuateindependently from the first.
 3. The method for cleaning a wafer asrecited in claim 1, wherein the first plurality of retractable tipscomprises 3 tips.
 4. The method for cleaning a wafer as recited in claim2, wherein each of the first and second drive mechanisms is one of ahydraulic, pneumatic, electromagnetic, or mechanical drive mechanism. 5.The method for cleaning a wafer as recited in claim 1, wherein eachmember of each of the pluralities of retractable tips is controlled byan independent drive mechanism and each of the independent drivemechanisms is connected to a controller.
 6. The method for cleaning awafer as recited in claim 1, wherein the first plurality of retractabletips comprises more than 3 tips and the second plurality of retractabletips comprises more than 3 tips.
 7. The method for cleaning a wafer asrecited in claim 1, further comprising extending a third plurality ofretractable wafer chuck tips from the wafer chuck in a directionsubstantially parallel to the axis of rotation of the wafer chuck toengage the edge of the rotating wafer with the third plurality of tips;and disengaging the second plurality of tips from the edge of therotating wafer after the third plurality of tips are engaged with theedge of the wafer.
 8. The method for cleaning a wafer as recited inclaim 1, further comprising engaging the first plurality of tips withthe edge of the rotating wafer; and disengaging the second plurality oftips from the edge of the rotating wafer after the first plurality oftips are engaged with the edge of the wafer.